There has been much discussion lately about Sonic Impact class-T digital amplifier. Since it is relatively inexpensive, I decided to give it a shot and evaluated it in my speaker system. After 100+ hours of breaking-in and no apparent changes in its sonic character for the last few days, I decided it is time to describe my experience with this little sonic wonder.

Integrated hybrid (tube/MOSFET op-amp) amplifier: Jolida JD 301A ($350; $310) + Yugo 12AX7
A lower-power (30W) version of better known Jolida models 1701A and 1501A. 301 is said to sound very similar to both except for perhaps slightly weaker bass. Audition Audition had a very positive review of 1501 that can be freely accessed, but the link is lost. I uploaded the review here (IE required) http://www.its.caltech.edu/~tai/JD%201501.mht

Quick Summary: Initially I was worried if built-in volume knob or less-than-perfect external power supply may negatively affect its sound. But I found these worries to be unnecessary. To my surprise, it never clipped during one week of testing in my room (13’ x 9’), partly because T-amp’s high resolution allows me to listen clearly at lower volumes.

Appearance: cheap plastic box weighing less than one pound

Front: Volume knob that also functions as power switch
I tried various things to determine if the volume knob can negatively affect sound quality. The answer is basically no. Comparing full-on versus 1/2 and 1/4 settings, using sources with variable outputs, sometimes full-on sounds better and sometimes worse. The difference is so subtle it could just be my imagination. After an exchange of posts with other head-fiers, I feel that the volume knob can have positive or negative effects depending on upstream and downstream equipment. I don’t think volume control quality needs to be a concern here, at least when it’s new and turning smoothly.

Back:
(1) Speaker connector: cheap spring clips.
The clips barely accept my 16 AWG wires. Forget about using banana plugs or spades, because they will never fit.
(2) Audio input: 1 x 3.5 mm stereo plug
If you are wondering why it is called a digital amplifier and only has analog input, then you should definitely read this article for clarification.http://www.audioholics.com/techtips/...mplifiers.html
Class T amplifier is just a variation of switching amplifier (Class D analog amplifier design) that has been around for a long time. The name “digital amplifier” is just a marketing phrase.
(3) Power adapter:
Accepts 5.5 mm OD/2.1 mm ID type DC connector between 12-14V, commonly found in wall warts. I am using booster battery for my car to operate T-amp, which happens to be here. It is essentially a 12V lead rechargeable battery. Since the amp is expected to run 6-12 h on 8xAA batteries, my booster should last 20 times longer. T-amp can require 2A at maximum output, while my battery can output 400A peak current and my DC cable has 5A fuse. Although lead battery can provide highest-quality DC, a 1.2A, 12V cheap wall wart does not seem to affect sound quality either. Maybe the highs are bit edgy with the wall wart, but it seems so subtle that it can be my imagination. If I don’t have the car booster, I would buy a 13.8 V, 3A Radio Shack power supply myself.

Bottom: Battery compartment for 8xAA, not tested.

Output power: Based on Tripath’s datasheet, it outputs 6 W per channel into 8 ohms, and 10W into 4 ohms. My speaker has 8 ohm impedance and is measured at 88.5 dB (anechoic/2.83V/1m) by Soundstage.com. My room is 13 by 9 feet and playing loud orchestral music is not an issue for T-amp. 6W is a lot less than what people are used to but enough for many situations. I also find myself listening at lower volumes on T-amp than my Jolida amp, possibly because T-amp has greater resolution and let me hear clearly at lower volumes. I haven’t experienced clipping on T-amp and can’t comment on what that would sound like.

T-amp driving headphones
Based on posts shared by fellow head-fiers, T-amp’s output level is too high for ordinary headphones and too low to be used with Antique Sound Lab UHC. Some kind of DIY attenuator/adapter is required to hook up ordinary phones to T-amp. Several head-fiers also reported that T-amp match quite well with K1000, and volume control does not seem to affect sound quality in such uses.

Mini-conclusion:
T-amp performs well as it is. It can be used as a power-amplifier or as an integrated amplifier with a single source. Its price and sonic performance (see below) makes it suitable for simple gaming systems all the way up to audiophile speaker systems.

Sonic Impressions: Sonic Impact T-amp vs Jolida JD301

Quick summary:
Within the confines of SI’s 6 meager watts, which are quite sufficient in my setup, it is a better amplifier than Jolida. Yes, that is a $30 amp outperforming a well-reputed $350 integrated amp. SI wins out mainly because of its resolution and transparency. SI also has tighter bass, faster attack, added presence and better imaging. In comparison, Jolida’s tube section lends itself to fatter bass, smoother highs and more diffused sound. SI’s highs seem brighter, and in some instances can be sibilant, thin or edgy. However, it is never harsh and nor does it present fake detailed feelings resulting from excessive treble. Its high frequency range contains a lot of musical information, but in my particular setup and room, it does not always render very well. Jolida’s tube nature makes more pleasant renditions than SI in certain situations, but on the musicality scale they score equally well. At the end of the day, SI brings me closer to the original performance and therefore it will replace the Jolida.

(1) About the Jolida
When researching on this unit, multiple online user comments indicate that Jolida JD 301 sounds better than entry level NAD integrated amplifiers (C320, C340 etc.). Unfortunately, I never had a NAD or Rotel in my home to compare to. Jolida has developed a very good reputation for great-bang-for-buck tube audio electronics in North America. JD 301 is a hybrid amplifier with two 12AX7 tubes and two LM1875 power IC. LM1875 also appears in the highly regarded 47 Labs Gaincard amplifier. I have Jolida sotck 12AX7, Yugo 12AX7 tubes, and TNT-selected Chinese 12AX7. Yugo is used in this review because it is what I generally prefer. Compared to Chinese tube, it is less resolving but more musical, but the differences are slight. Stock tubes are clearly inferior. Bill Baker of Response Audio actually thinks quite highly of JD301 and once marketed a modified version of it called RAM 301.

(2) Setup:
Evaluations are done on CDs with the Sony as Transport and the Benchmark as DAC.
T-amp (powered by voltage booster) is connected to Benchmark’s headphone out. Volume knob is fixed at 1/2 on T-amp and actual volume control is performed by Benchmark. I feel this configuration gives most smoothness for the combo, which is preferred.
Jolida is connected to Benchmark through RCA output in fixed mode (maximum voltage level). Volume control is performed on Jolida. I feel this configuration gives best resolution for the combo, which is preferred.

(3) Music:
I listened to many CDs on each amp, and here is a list of CDs that best illustrate their differences.

b. What about this Mr. Paganini? Violins of Amati, Guadagnini, Guarneri, Hovarth, Stradivari, Vuillaume (Tacet 36)
Amazingly realistic (through Benchmark and K501) recording of seven great violins compared side-by-side. Since I played the violin as a child and often hear it in concerts, I use this disc to evaluate the highs. Admittedly, my Athena speakers do not reproduce believable violin notes, especially the higher ones. I think Athena is a bit dark and grainy compared to K501. Jolida’s tubes add roundedness to violin’s high notes, which is enjoyable. SI actually differentiates the sonic characters of each violin better, but all of them sound a bit edgy. This is not to say SI generally sound brittle in high frequency, because high piano notes sound better on SI. Jolida gets the nod on smooth violin sound.

c. The Ultimate Demonstration Disc: Chesky’s guide to critical listening (Chesky UD95)
It is an invaluable disc for audiophiles, because each musical track is preceded by an explanatory narrative track on what to listen for. It tells me what to expect if my system is near-perfect, so I don’t have to guess. Using tracks 5 and 23, I find no discrepancy in three-dimensionality of these two amps, either in soundstage depth, width or height. On track 23, a choral recording in a big cathedral, both recordings show astounding soundstage height. On SI, the beautiful reverberations make me think they are reflected from stone, which is probably the actual case. On Jolida, the sound is softened and diffused so it sounds like a tall wooden hall—less real but more fun. IMO this is a great example of how these two amps voice in different but equally valid ways. Track 7 shows that SI produces cymbals more clearly than Jolida. SI gets the nod on extreme high frequency.

d. Rebecca Pidgeon: Retrospective (Chesky hybrid SACD, SACD242, CD layer used for evaluation)
Track 1 (the famous Spanish Harlem) is the remastered version of previous CD’s track 3. SI has tighter bass that is more realistic compared to Jolida’s fatter bass. Maraca is heard very clearly on both, showing that neither lacks details. However, SI separates maraca more clearly from other instruments and defines it better in space. Track 3 is very beautiful and simple female vocal. SI renders it with pleasant sibilance. Jolida makes it darker and fuller. Not knowing what Rebecca’s real voice is like, I can only say they are equally enjoyable. SI gets the nod on bass, imaging and resolution.

e. The New Tango: Astor Piazzolla and Gary Burton (Atlantic 781823-2)
This is the most surprising find of the day. I always thought it is a mediocre early digital recording (1987), because it sounds kind of muffled with Jolida. It sounds cleaner through K501 headphones, but still not impressive. But this recording really wakes up with SI. Through SI, it shows a lot of presence, which is probably a combination of clean sound, good stereo mixing to create imaging and airiness, and some forwardness. SI gets the nod on presence.

(4) Further sonic comments
T-amp is simply great for its resolution, not just great for its price, but just great per se. K501 and Benchmark’s headphone output is not the last word in resolution, but it is certainly very good. T-amp and Athena speakers, connected to the same headphone output, give almost as much resolution. I assume Athena S2 is not as resolving as K501, and therefore I guess T-amp basically causes no loss in resolution. The only negative thing I observed during T-amp testing is that solo violin passages sound edgy. At the same time, T-amp outperformed Jolida in other high frequency areas such as piano, vibraphone and cymbal. This leads me to suspect that my speakers are actually responsible for the violin glitches I hear. Jolida’s tubes certainly cover up this better, but with T-amp I am also able to modify my room acoustics and tweak with speaker grilles to make much of the glitch disappear. T-amp is brighter than Jolida (tubed), but I suspect all solid state stuff is. I don’t know if T-amp is bright on an absolute scale, because I don’t have megabuck speakers and amplifiers to serve as references. In the mids and lows, T-amp excels at everything I threw at it. Although T-amp looks lightweight, it produces a weighty sound--cello has a surprising degree of realism on SI/Athena combo. In the highs, it still outperforms Jolida, but my system admittedly isn’t hi-end enough to determine its actual shortcomings, which may or may not exist.

Mini-conclusion:
In terms of tonality and voicing, SI and Jolida are philosophically different. T-amp offers what I would expect in a good solid state amp: transparency, speed, attack, rhythm, presence, and some brilliance. Jolida uses good, old 12AX7 to soften the sound, which is quite preferable in some situations. But SI simply has more resolution and detail, so it comes out as the winner. Jolida is falling behind in terms of fidelity, but the musicality of both amps is excellent.

Final Conclusions:
Even when T-amp is used with cheap cables and wall-wart, its performance is still a level above my beloved Jolida. In my experience, cleaner power supply can improve the sound a tiny bit. Its built-in volume can make it sound a bit better or worse based on upstream or maybe downstream equipment. T-amp’s great resolution allows listening at slightly lower levels, and therefore its 6W is very sufficient for my use. T-amp really works as advertised, and its ease of use gets a “10” on my scorecard. During my one week evaluation, T-amp did most things right and if I had find fault it would be a few minor glitches in the highs. To be fair, my speakers and older amplifier, though much more expensive than T-amp, are not hi-end enough to help me identify whether the glitches I hear actually come from the T-amp. I consider T-amp a piece of genuinely hi-end gear, just like my Benchmark DAC1 and AKG K501. For $30 it truly is a no-brainer. I would strongly recommend it for simple computer speaker setup all the way up to hi-end speaker systems.

Pros: bargain-basement price, sonic strengths of very good solid state amps, ease of use, relative insensitivity to cheaper connections and power supply, small footprint.

Cons: None for its asking price.
Compared to hi-end amps: lower power and cheap connectors.
Sonically, I can’t identify apparent faults. If I have to guess, it would be some sibilance in highs and the volume control can change its sonic properties a tiny bit (for better or worse seems setup-dependent).

More thoughts on the T-amp:
After one week with the T-amp, I have to ask myself, how can such a cheap amp sound this good? Here is my educated guess. Class-T amplifier IC is new class of chip design aimed at providing good sound. Given the advances of semiconductor technology, it is not surprising that ICs can also improve in terms of sound quality. Bel Canto’s new digital amplifiers also use class-T chips and I have heard nothing but praise for them in audio magazines. Usually, designing hi-end electronics requires careful tuning of the circuitry to improve the sound. Still, without such hi-end purposes in mind, sometimes a piece of mass-market electronics can be designed right on the mark to sound really good. I think this is what happened with T-amp. Sonic Impact products are designed for ipod users. But most ipod users have no need for a 6W amp because they don’t buy passive speakers. I am not sure if T-amp is selling that well, because few on-line stores carry it. I am worried if T-amp will go out of production soon. I am actually considering buying a second T-amp and preserve it for later use. I would recommend audiophiles even remotely interested in this amp go out and grab one right now.

Nice review I am remotely interested in this amp mainly to replace my vintage Kenwood KR3600 reciever that gives about 18 wpc, and at $30 this might be what I'm looking for since I don't do anything beyond 2 channels. However I was wondering would this amp be fit for my speakers? They are rated at 8 ohms, 89db, and maximum power is 150 watts. Thanks!

Hell, go out and buy several. I'm still kicking myself for not buying 5 of these at the $6 price I got the one for. I was too cheap to pork over $30 for 5 of'em without an audition. Oh, well, that ship has sailed.

Even with Athena speakers, you probably are not getting the best out of SI even though there's no clipping. Most amps really do put out much better power with their first watt or two, which translates into around 95-96 dB efficient speakers to play moderately loud with 1 watt or so.

With a good power supply and K1000, the SI puts out enormous power and authority that I've often heard with speaker systems employing multi monoblocks of 600-1000 watts..

Nice review I am remotely interested in this amp mainly to replace my vintage Kenwood KR3600 reciever that gives about 18 wpc, and at $30 this might be what I'm looking for since I don't do anything beyond 2 channels. However I was wondering would this amp be fit for my speakers? They are rated at 8 ohms, 89db, and maximum power is 150 watts. Thanks!

oh ya its ognna be used in a small room

The rule of thumb is that speakers sound needs to reach 110 dB if you want to reproduce true loud concerts. In reality, 100 dB is probably enough, and 95 dB is barely adequate.
If you have 89 dB, 8 ohm speakers, 1W power would create 89 dB at 1 m distance. Now you have a pair, add 3 dB. With room reflections, add 3 dB. If you sit 5 feet away, subtract 3.5 dB. And consider 6W maximal output, add 8 dB. 89+3+3-3.5+6, you get 97.5 dB. That is quite probably sufficient except for the loudest music. 6W is only 5 dB below 18W. I think you are not going to notice much of a difference if you switch to T-amp.

i amaze myself at my restraint, especially since i just got some wharfdales to be powered. but seeing as how i have a sub incoming, and i need to use my receiver (or 1911's) as a phono stage too, shelling out any kind of bucks for something like this wont make sense. unless i had a K1000.

I just find the idea that a $30 amplifier is beating a quality $350 receiver to be exciting.

I can't wait to see what the DIY'ers will be able to do with one of these, or maybe Sonic Impact themselves will release a a version of their amp that does 50 watts per channel and is made of higher quality materials. They have to have a profit on the amp now, they could jack up the price to $200 for a 100 watt amp and audiophiles would buy it because it would still be the best bang for the buck out of anything at all out there.

I agree with this review. I have also found some silibance and the highs a bit "hard". Midrange resolution excellent and the bass adequate. However, I've enhanced it's performance by feeding a sound card digital signal to an ART DI/O which gives the needed punch to the bass and then feeding the output to a x-can v2 which acts as a preamp before the t-amp. The x-can smooths out the hard highs. The result: a very, very, good sounding t-amp which drives a B&W DB302 speaker to a reasonable sound level. The T-amp is an absolute best buy and recommended for anyone wanting a quality sounding amp for the lowest possible cost. Next, I'm going to try it out as a headphone amp. I have this 2-way speaker switch box by Bryston which has a headphone jack.

I had to buy the soundpax system in order to get the t-amp. It seems the amp by itself is backordered by everyone. The soundpax speakers are good value for the money but they're not very elegant. Some spouses would find them unattractive in their living room decor -- at least mine did.

However, I've enhanced it's performance by feeding a sound card digital signal to an ART DI/O which gives the needed punch to the bass and then feeding the output to a x-can v2 which acts as a preamp before the t-amp. The x-can smooths out the hard highs. The result: a very, very, good sounding t-amp which drives a B&W DB302 speaker to a reasonable sound level.

I agree with you observation of using a hedphone amp as preamp for T-amp.
Both my Benchmark DAC1 and Sony SACD/DVD player have headphone and RCA outputs. To my ears, using the headphone output makes the highs a tiny bit smoother compared to RCA out on both sources. I don't know why.

Quote:

Originally Posted by mail4u

Next, I'm going to try it out as a headphone amp. I have this 2-way speaker switch box by Bryston which has a headphone jack.

I look forward to hearing how well this switcher box works for headphones. I think many head-fiers are wondering if T-amp can act as a normal headphone amp with the right adapter. How does this headphone jack work in the Bryston? Is it transformer based?

Ferbose, I just tried the switcher box headphone output and compared it to the x-can phone output. The x-can destroys it. It's much cleaner and has wider sound stage. It looks like the Bryston switcher is of the transformer type, and it is the culprit of the degradation of the sound. It is my feeling the t-amp as a headphone amp in itself is not the equal of the x-can. I much prefer the x-can with HD 580s to the t-amp driving the B&Ws. Make no mistake about it, the t-amp is good sounding but not in the same league. It's missing that "air" of x-can tubes even when the x-can is used as its preamp. That is, it must be degrading the input from the x-can.

Even if it did produce the equivalent sound quality to the x-can, it wouldn't be much of a cost saving. Bryston is listing the switcher for $199. I got mine for $65 Canadian, nine years ago.

It is my feeling the t-amp as a headphone amp in itself is not the equal of the x-can. I much prefer the x-can with HD 580s to the t-amp driving the B&Ws. Make no mistake about it, the t-amp is good sounding but not in the same league. It's missing that "air" of x-can tubes even when the x-can is used as its preamp. That is, it must be degrading the input from the x-can.

To my ears, HD580 sounds much better than entry level B&W speakers, especially those 300 and 600 series ones, in terms of clarity, details, tonality and all those areas where cans should excel. To get the clarity of HD580, I suspect you need to go up to B&W 800 series. Therefore it is not surprising x-can+HD580 can sound better than T-amp+B&W. And Bryston's headphone adapter may not be very good or may not be designed for flee-powered amps, so it is not a true comparison between x-can and T-amp's sound quality. In mikeg's post, he reported that T-amp beats $6800 pream+amp combo for driving K1000. T-amp is a power amplifier and a direct comparison of it to a headphone amplifier is very difficult, because they are designed to drive very different loads.

I would spend $200 for such a product if it was encased in a decent-looking chassis that included a quality linear power supply and preferably a detachable power cord - this could be the ultimate K1000 amp.